Engine Management Light - What Does It Mean and What Should I Do?

Has your engine management light come on? Don’t worry - read on to find out what it could mean and what you should do. 

Even the most reliable of cars suffers the occasional jitter, and your vehicle’s way of telling you it needs some attention is often by displaying a warning light. 

There are several different warning lights, each relating to a different issue. The engine management light is often seen as one of the most concerning, and ignoring it could lead to costly damage - so it helps to arm yourself with some useful knowledge in case it lights up. 

Our guide tells you everything you need to know about the engine management light - what it is, what can cause it to come on and what you should do if it does.

What is the engine management light?

The engine management light - also called the check engine light - is one of a number of warning lights you’ll find on your car’s dashboard. 

You’ll see it illuminate briefly when you start your car along with all the other dashboard lights - it usually looks like an engine outline, or may show the words ‘check engine’. If it stays on or lights up while you’re driving, it may indicate there’s an issue that needs attention. 

The engine management light is connected to your car’s engine control unit (ECU). This is your car’s electronic ‘brain’. The ECU helps the engine run smoothly by controlling things like the ignition timing and air-fuel ratio. 

The ECU has a number of sensors placed around the engine and exhaust. If one of these determines that a component or system is malfunctioning, it will prompt the engine management light to come on. 

Unlike some of the other warning lights, the engine management light doesn’t point to a single specific fault. There are a number of different issues it could indicate, some more serious than others. 

While not all of these issues will cause your engine to blow up, they could cause significant damage further down the line if ignored - so it’s well worth getting the problem properly diagnosed.

What do the different colours mean?

Many cars display the engine management light in different colours depending on the severity of the problem. 

Your vehicle handbook should tell you what your car’s specific colour system means, but we’ve listed the typical definitions below:

  • Solid amber light: A solid amber engine management light is an advisory warning, usually pointing to an issue affecting exhaust emissions. In most cases it won’t be an emergency, so you should be able to finish your journey - but you should get it checked out as soon as you can before it develops into anything more serious. 
  • Flashing amber light: A flashing amber light often indicates a misfire, which may make the engine sound harsh and the car judder. If you carry on driving the engine may overheat, causing expensive damage - so you should drive at a reduced speed to a garage straight away. 
  • Red light: A red engine management light indicates a serious fault, so you should stop as soon as it’s safe to do so and call your recovery provider. Driving any further without having it checked could cause serious damage.

Will my car pass its MOT if the engine management light is on?

MOT rules became stricter in 2018, meaning that a car will automatically fail if it has an illuminated engine management light during its MOT test. 

Check your warning lights before you take your car for an MOT - if the engine management light stays on once the engine is running, get it checked out.

Diagnosing the problem

When the ECU prompts the engine management light to come on, it also generates an error code that indicates what the specific issue is. 

When a vehicle technician investigates the problem, they’ll download these codes using a reader that plugs into a data port on the car. You can buy one of these readers yourself, and they’re usually universal, so you can use them with any car. Once you’ve got the codes you can use your car’s manual to find out what they mean. 

However, a DIY diagnosis won’t always result in an accurate answer or an easy fix. Sometimes the error code will reveal a symptom but not the cause, so a solid knowledge of vehicle diagnostics would be required to work out what needs to be done. 

In addition, some car manufacturers use extra codes that can only be downloaded using specialist readers - so you may miss important information with a universal reader. 

Getting it checked out by a professional is the most reliable way to diagnose the problem. Below, we’ve listed 10 common reasons your engine management light may come on.

10 common causes for an engine management light

1. The petrol or diesel filler cap is loose

This fault carries a low risk of damage and is one of the simplest and cheapest to fix. 

Your fuel tank is a complex pressurised system: as fuel is pumped into the engine, the space it took up in the tank is replaced by air. Without air taking the fuel’s place, the pressure would simply crush the fuel tank. 
 
Metered quantities of air are allowed into the tank through a vent as the fuel is pumped out. The fuel tank air pressure sensor determines how much air should be let in - but its readings will only be accurate if the tank system is pressure tight. A loose or faulty filler cap may allow extra air in, thus throwing the sensor off. 
 
If the sensor can’t provide an accurate reading it will trigger an engine management light. To fix the problem, check or replace your fuel filler cap.

2. The vacuum hose is leaking 

This is another issue with a relatively low risk. 

Vacuum hoses are used to route vacuums around the engine to various components. Older vehicles are likely to rely on vacuum hoses more - modern vehicles tend to have fewer of them as more systems are now computer controlled. 

Most vacuum hoses are made of rubber, so they tend to deteriorate over time. If one of them leaks, it can set off the engine management light. To fix the issue, take your car to the garage and have any faulty hoses replaced.

3. Oxygen sensors 

Again, this is a low-risk issue. 

Modern cars tend to have at least two oxygen sensors, which measure how much air leaves the engine through the exhaust system. If the sensors return an abnormal reading they can set off the engine management light. 

To fix this problem, you should take your car to the garage to be serviced.

4. Mass airflow sensor 

This is another problem with a lower risk of causing damage. 

While the oxygen sensors monitor the air leaving the engine, the mass airflow sensor measures how much oxygen comes in. 

If there’s not enough oxygen coming in, the engine will run poorly. It may also affect exhaust emissions, although this might not be immediately discernible. 

A common cause of reduced airflow is a blocked air filter. Air filters should be replaced periodically - check your car’s manual to see how often this should be done.

5. The exhaust gas recirculation (EGR) valve is faulty 

This fault also falls into the lower risk category. 

Most modern diesel vehicles are fitted with an EGR valve, which plays an important role in reducing harmful emissions. 

The EGR system works by recirculating up to 15% of exhaust gases back into the engine, which lowers the oxygen level and increases the water vapour content in the combustion mixture. This reduces the peak combustion temperature, which in turn reduces nitrogen oxide emissions. 

The EGR valve regulates the amount of exhaust gas being returned based on the engine load. The valve can become clogged by a buildup of carbon deposits, which can cause it to stick either open or shut. 

If this happens, the engine management light will come on, and you should have your car serviced at a garage.

6. The fuel pump is faulty 

This issue carries a medium risk of damage. 

Your car’s fuel pump sends fuel from the tank to the engine at the required pressure. If there’s a fault with it, the delivery of fuel will be hampered and your engine will run poorly, have trouble starting or not start at all. 

In this case the engine management light will come on, and you should have your car checked out.

7. The fuel injectors are blocked 

This is another medium-risk fault. 

The fuel injectors spray fuel into the engine’s combustion chamber. This process is regulated by the ECU. The angle the injectors are placed at, the fuel spray pattern and the pressure at which it’s delivered all need to be very precise in order to achieve the correct air-fuel ratio for combustion. 

Over time, fuel injectors can become dirty or blocked by fuel deposits. If this happens it can cause a noticeable decrease in performance, or the engine may misfire. It will also trigger an engine management light, and you should get it checked out at the garage.

8. The ignition system is faulty 

Again, this is a medium-risk issue. 

The ignition system generates a high voltage from the car’s 12v battery and sends it to the sparkplugs, which create a spark that ignites the fuel-air mixture in the combustion chambers.

In a petrol engine, faults can occur with the system that controls the timing of the spark, or with the coil (the component that generates the high voltage). If a problem arises you may feel the engine misfiring. This is risky, as it can cause expensive damage to the catalytic converter - so you should take your car to the garage as soon as possible.

9. The particulate filter is clogged 

This issue comes with a high risk of damage. 

Diesel vehicles have had particulate filters for years, but as emissions limits become more stringent some petrol cars are being fitted with them as well. 

Particulate filters work by trapping and storing exhaust soot in order to reduce harmful emissions. On diesel vehicles the filter can become clogged, at which point the particulate filter warning light may come on. You may then need to drive the car at higher speeds for a short period in order to burn off the excess soot. 

If you don’t, the problem can be exacerbated and the engine management light may come on. This is often because of the alteration to the engine’s oxygen supply. You should get the problem fixed as soon as you can, because a new particulate filter can be very expensive. 

Petrol particulate filters are much less prone to getting clogged up as petrol engines run hotter than diesel engines, which means they burn off more of the soot.

10. The catalytic converter is contaminated 

This is another high-risk issue. 

The catalytic converter is the most important part of your car’s emission control system. It converts toxic substances in exhaust gasses (like hydrocarbons, carbon monoxide and nitrogen oxides) into less harmful substances like water vapour and carbon dioxide. 

It does this by way of chemical reactions catalysed by precious metals like palladium, rhodium and platinum. 

Over time, catalytic converters can become contaminated by oil and coolant that have leaked into the engine, or get clogged up by a buildup of carbon deposits. This restricts the passage of exhaust gasses and consequently reduces airflow to the engine, which can result in a drop in efficiency. 

This can cause the engine management light to come on - at which point (you’ve guessed it) you should take your car to the garage as soon as possible.

The Engine Management Light: Conclusion

These are some of the most common reasons your engine management light might come on, but there are plenty more - so if yours lights up, get it checked out as soon as you can. 

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